1. (Field of the Invention)
This invention relates to an electrode for an electric double layer capacitor and a method of manufacturing the same and, more particularly, to an electrode for an electric double layer capacitor optimum for obtaining a large electrostatic capacity and a method of manufacturing the same.
2. (Description of the Prior Art)
Recently, an electric double layer capacitor using the storage of charge based on an electric double layer, i.e., a principle of an electric double layer has been developed and manufactured. Since this capacitor can obtain a large electrostatic capacity, the small-sized capacitor has been used for a back-up power source of a semiconductor memory for an electronic equipment and the large-sized capacitor has been used for the part of the utilization of an on-vehicle lead battery.
A method of manufacturing a molded unit of activated carbon comprising the first step of pressurizing carbon powder mixed with water under pressure of 50 kg/cm2 while heating the carbon powder to obtain powder activated carbon, and the second step of pressure molding the resultant powder activated carbon under the pressure of 50 to 800 kg/cm2 at a temperature of 700.degree. to 1,000.degree. C. to obtain the molded unit of the activated carbon as an electrode material for the electric double layer capacitor of this type was disclosed in Japanese Patent Application Laid Open No. 3-201,520(1991) by the same assignee as the present invention.
As a result of the research and development of an electrode for an electric double layer capacitor, the applicant of the present invention has also developed an electrode material in which pores are formed by heating polyvinylidene chloride resin in a non-oxidizing atmosphere and thereby generating atomic and molecular defects, and filed Patent Application Laid Open No. 7-24955 (1994). This material showed in the above Laid Open document is formed of a porous carbon material having very fine pores, which is an electrode material of much higher capacity than that of the conventional activated carbon.
Since the carbon powder is used as a starting material in the molding method disclosed in the above-described Japanese Patent Application Laid Open No. 3-201520 (1991), its volatile component which contributes to its solidification has been evaporated in the step of carbonizing, and hence difficult to be solidified. Thus, in the case of molding, large power or large energy is required. Hence, its manufacturing cost is high. Further, this method also has a problem of difficulty of increasing the molding density. In order to solidify the carbon powder, when binder is used, its electric capacity is reduced that much of the binder in the case of manufacturing the capacitor. When the resin of the material of the carbon is pulverized as it is, then molded and thereafter sintered, its volatile component is excessively much, and hence its shape cannot be maintained. Because the volatile component is evaporated in a large quantity at the time of baking, and its shape is collapsed by its evaporative power.
In other words, according to the conventional method, the volatile component is excessively much or little and not suitable, and hence the carbon powder cannot be sufficiently solidified.